Essential Chemistry Definitions: Matter, Elements, and The Mole

Fundamentals of Chemistry

Chemistry is the science that studies the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions and its relationship with energy.

Defining Matter and Its Properties

Matter is anything that occupies space, has measurable energy, and is subject to change over time and interactions with measuring devices.

States of Matter

• Solid: If the kinetic energy is less than the potential energy.
• Liquid: If the kinetic and potential energy are approximately equal.
• Gas: If the kinetic energy is greater than the potential energy.
• Plasma: If the kinetic energy is such that the electrons have a positive total energy.

Chemical Elements and Atomic Structure

A Chemical Element is a type of matter consisting of atoms of the same class. In its simplest form, it has a certain number of protons in its nucleus, defining its category by the atomic number, although it may possess different atomic masses (isotopes).

Key Subatomic Particles

• Electrons: Leptonic particles with a negative electrical charge.
• Protons: Baryonic particles with a positive electric charge.
• Neutrons: Baryonic particles with no electric charge (but possessing a magnetic moment).

Molecules, Compounds, and Mixtures

A stable Molecule is an electrically neutral whole consisting of at least two atoms linked covalently.

A Compound is a substance formed by the chemical union of two or more elements from the periodic table. An essential feature is that it has a defined chemical formula.

A Mixture is a material system consisting of two or more pure substances that are not chemically combined. In a mixture, no chemical reaction occurs, and each component retains its identity and chemical properties.

Quantitative Chemistry Concepts

The Mole (Amount of Substance)

The Mole is defined as the amount of substance that contains as many elementary entities as there are atoms in 12 grams of carbon-12.

Atomic Weight and Molar Mass

Atomic Weight (symbol: A_r) is a dimensionless physical quantity defined as the ratio of the average mass of the atoms of an element (from a given source) to 1/12 the mass of one atom of carbon-12.

Molar Mass (symbol M) of an atom or molecule is the mass of one mole of the particle expressed in grams. It is a characteristic physical property of each pure substance.